As disclosed in Japanese Laid-Open Patent Application Publication No. 2007-247518, an engine unit mounted in a vehicle such as personal watercraft sometimes includes a supercharging machine such as a mechanical supercharger or a turbo charger (exhaust turbine supercharger).
Typically, a main body of the supercharging machine is directly mounted to a side surface of an engine body. In such a construction, since a vibration of the engine is directly transmitted to the main body of the supercharging machine, it is necessary to increase stiffness of the main body of the supercharging machine and resistance of components within the main body to the vibration.
During running of the engine, typically, a temperature of the main body of the supercharging machine tends to be higher than a temperature of the engine body, and therefore, the main body of the supercharging machine tends to be thermally deformed and expanded in an amount larger than the engine body due to a difference in expansion coefficients between the main body of the supercharging machine and the engine body. In order to avoid that the thermal deformation of the main body of the supercharging machine and the thermal deformation of the engine body affect each other, it becomes necessary to increase rigidness of the main body of the supercharging machine and the engine body, for example. Furthermore, since the heat tends to be transferred from the main body of the supercharging machine to the engine body, it is difficult to cool the engine body.